Process for manufacturing granules containing sodium chlorite in a fluidized bed drier

ABSTRACT

A process for the manufacture of granules containing sodium chlorite from an aqueous medium containing sodium chlorite, including the steps of passing the medium into a fluidized bed drier for evaporating water from the medium, and maintaining in the drier a constant presence of seeds smaller than the required granules.

United States Patent [191 Denaeyer et al.-

[451 Oct. 29, 1974 PROCESS FOR MANUFACTURING GRANULES CONTAINING SODIUMCHLORITE IN A FLUIDIZED BED DRIER [75] Inventors: Jos Luis Denaeyer;Willy Kegelart,

both of Brussels, Belgium [73] Assignee: Selvay & Cie, Brussels, Belgium[22] Filed: Apr. 12, 1972 211 Appl. No.: 243,252

Related US. Application Data [63] Continuation-impart of Ser. No.106,546, Jan. 14,

1971, abandoned.

[30] Foreign Application Priority Data Apr. 13, 1971 Belgium 102099 [52]US. Cl 23/301 R, 23/302, 23/313, 423/472 [51] Int. Cl B0ld 9/00, C01b11/10 [58] Field of Search 423/473, 472; 23/313, 300 C, 23/301 R, 302

[56] References Cited UNITED STATES PATENTS 2,520,915 v 9/1950Cunningham 423/472 2,567,959 9/1951 Munday 23/313 3,006,721 10/1961Mollard 23/313 3,231,413 l/l966 Berquin r 23/313 FOREIGN PATENTS ORAPPLICATIONS 332,705 ll/l903 France 423/473 OTHER PUBLICATIONS C & En,Dec. 26, 1960, Britain Starts Making Na- ClO2, page 40. Forbath, ChemEng., pages 180-182, June 12, 1961, Vol. 68, 12.

Primary Examiner-Wilbur L. Bascomb, Jr. Assistant ExaminerS. J. EmeryAttorney, Agent, or Firm--Spencer & Kaye 5 7] ABSTRACT A process for themanufacture of granules containing sodium chlorite from an aqueousmedium containing sodium chlorite, including the steps of passing themedium into a fluidized bed drier for evaporating water from the medium,and maintaining in the drier a constant presence of seeds smaller thanthe required granules.

6 Claims, 3 Drawing Figures Pmmeow 29 mm FIG. I

FIG. 3

PROCESS FOR MANUFACTURING GRANULES CONTAINING SODIUM CHLORITE IN AFLUIDIZED BED DRIER CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OFTHE INVENTION The invention relates to a process for manufacturinggranules containing sodium chlorite by drying an aqueous mediumcontaining chlorite in a fluidized bed permanently containing seedssmaller in size than the required granules.

Technical literature contains references to various processes forpreparing solid sodium chlorite from a solution or, generally, anychlorite containing aqueous medium. Crystallization is the first stagein one of these processes and this may be followed by centrifugalseparation and drying of the crystals (see, for example, US. Pat. No.2,520,915 of Apr. 26th, 1945, in the name of DIAMOND ALKALI CO). Inanother process, which has become a standard procedure, drying iseffected by atomization (cf. the .article by T. P. FORBATH in ChemicalEngineering, 1961, 68, No. 12, pp. 180-182), the end product being afine crystalline powder. Rotary drum driers heated internally by steamtubes and supplied with product by a prethickener (cf. FIAT report,Final Report No. 825, chlorine dioxide and sodium chlorite at I. G.Farben, Griesheim, p.4) are also used. Here, the end product is in flakeor fine crystal form. Occasionally, the chlorite is dried in severalstages at progressively increasing temperatures (cf. Belgian Pat. No.452,924 of Oct. 22nd, 1943, in the name of Solvay & Cie). Manufacture ofsodium chlorite granules in which the first stage is preparation oftrihydrate crystals by evaporation under vacuum, then followed by fusingindividual crystals and arranging them in the form of a fluidized bed ina solution saturated with chlorite, or even drying the surface of thetrihydrate crystals with a stream of inert gas (French Pat. No.1,187,352 of Nov. 29th, 1957, and French Pat. No. 1,228,234 of Mar.10th, 1959, both in the name of SOCIETE DELECTROCHIMIE, DELEC-TROMETALLURGIE ET DES ACIERIES DUGINE) has also been suggested. Lastly,there have been references to the fact that use of a fluidized bedprocess for drying trihydrate crystals is beneficial. (A. 1. KA-

CHALOV Khimicheskaya Promyshlennosti, 1960,

pp. 336 to 339).

Owing to the comparatively large number of chemical operations involved,most of these processes are extremely laborious. Finally, others such asthe atomization or rotary drum processes produce chlorites in powder,fine crystal, or flake form which do not meet the criteria of manycustomers.

SUMMARY OF THE INVENTION An object of the present invention, therefore,is to provide a process for preparinga solid, dehydrated sodium chloriteproduct in the form of granules of predetermined size in a singleoperation starting from an aqueous medium containing sodium chlorite.

This as well as other objects which will become apparent in thediscussion that follows are achieved, according to the presentinvention, in a process for manufacturing granules containing sodiumchlorite from an aqueous medium containing sodium chlorite,characterized in that water from the aqueous medium is evaporated on itsbeing introduced into a fluidized bed drier, drying being effected inthe constant presence of seeds the dimensions of which are smaller thanthose of the desired granules. The seeds may be particles of sodiumchlorite or any substance compatible with sodium chlorite.

GENERAL ASPECTS OF THE INVENTION Application of similar processes to themanufacture of extremely diverse products, particularly fertilizers,sodium sulphate, zinc sulphate, sodium chloride, calcium chloride,caustic soda, etc., has been known for some time. However, to ourknowledge, it has never been suggested that such a process should beapplied to the preparation of granules containing sodium chlorite from asolution or other aqueous medium. This is undoubtedly due to thepotential difficulties raised by the sensitivity of chlorites totemperature and shock.

The process per the invention can be implemented either continuously ordiscontinuously. It is used for treating solutions containing chloriteand possibly other compatible substances, preferably concentratedsolutions or aqueous suspensions obtained after prethickening, forexample. The aqueous medium containing chlorite is passed into afluidized bed drier, either into a zone located above the bed, or withinthe fluidized bed.

The fluidized bed of chlorite particles must always contain seedssmaller than the required granule size, as these seeds are to receivenourishment from the chlorite liberated by the aqueous medium. Asalready mentioned, these seeds may consist of sodium chlorite particlesor particles of another substance compatible with the chlorite, such asparticles of sodium chloride, sodium nitrate, sodium carbonate, etc. Thesupply of seeds for the fluidized bed may come from an outside source,from a crusher, for example, or may be formed in situ. We prefer thelatter owing to the sensitivity of chlorite to shock. The fluidized beddrier is merely equipped with a mechanical arrangement for breaking upthe granules, a stirrer or scraper, for instance, fitted in the midst ofthe fluidized bed. The seeds can also be formed by atomizing the aqueousmedium containing chlorite under conditions such that it reaches thefluidized bed in the form of individual particles or droplets. Anystandard arrangement, such as a nozzle, can be used for this purpose.

The seeds can also be produced in situ by breaking particles already inthe bed mechanically, by selecting an adequate atomizing gas flow rate.

We have observed that the sodium chlorite particles in the fluidized bedtend to compact and that this may, in some cases, lead to completeagglomeration of the bed and thus to a risk of chlorite thermaldecomposition. This disadvantage can be overcome by fitting a stirrer, awiper, for example, at the bottom of the drier. The purpose of thisarrangement is twofold: to prevent the bed from compacting and toprepare seeds by breaking up some of the granules mechanically.

The temperature of the air or other carrier gas introduced at the baseof the fluidized bed, for example,

through fabric or a distribution plate, should preferably be underapproximately 180C and operating conditions should be adjusted such thatthe temperature inside the fluidized bed does not exceed 80C.

The fluidized bed drier can be cylindrical, cylindroconical,parallelepipedic or any other shape suitable for application of theprocess.

The chlorite granules can be discharged by any recognized means, forexample, via the base of the drier under elutriation or via a lateraloverflow pipe, this pipe thus determining the height of the fluidizedbed.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional elevationalview of a fluidized bed drier suitable for use in the present invention.

FIG. 2 is a view of a modified fluidized bed drier from the line 2 2 ofFIG. 3.

FIG. 3 is a view of the drier of FIG. 2 from the line 3 3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a suitablefluidized bed drier for carrying out the process of the invention.Clamped be tween cylinder 1 and air guide 2 is a unit 3 which has thefunction of uniformly distributing in the cylinder the air flowing intothe guide 2 in the direction of arrow A. The air flowing from the unit 3into the cylinder creates a fluidized bed 4 of particles. Nozzles 5a, 5bare provided for the spraying of aqueous medium into the fluidized bed.Lateral tubular outlet 6 continually draws off particles from thefluidized bed.

Various embodiments assure a constant presence of crystallization seeds.

It is possible to continuously supply the drier with crystallizationseeds through a tube 8 from a bin 9.

In accordance with another interesting embodiment, the particles whichare used as seeds to form new granules are formed by mechanicallydestroying inside the fluid bed drier a portion of the granules alreadyformed. For this purpose, the fluid bed drier may be provided withdevices such as agitators, crushers, scrapers, etc. which can operatecontinuously. FIGS. 2 and 3 illustrate an embodiment where a scraper isused. The scraper, part 10 in FIGS. 2 and 3, is connected rigidly toshaft 12. Motor 13 thus can move the scraper continuously around theinner periphery of cylinder 1. The scraper removes and comminutesbuild-up on the bottom of the cylinder and additionally traps freeparticles between itself and the wall of the cylinder and comminutesthem.

Further illustrative of the invention are the following examples:

EXAMPLE I The drier used consists of a cylinder 15 cm in diameter and 60cm high, the base of which is fitted with a plate for distributing thegas. The plate is topped with a stainless steel gauze of 3 mm mesh. Ascraper fitted with small flexible stainless steel blades rotates onthis gauze at a rate of 250 to 300 revs/min. The granules are dischargedfrom the bottom of the bed via a pipe 15 mm in diameter intowhich'passes a draught of cold elutriation air at the rate of 3 standardm /hr. The particle bed is fluidized by passing a blast of air (53standard.

gm/kg of solution NaClO; 326

NaClO 5 do. NaCl 86 1 do.

Na CO 9 do. NuOH 5 do.

passes at the rate of 3,300 gm/hour and at 35C.

As soon as the plant is fully operational, 1.40 kg/hr of a producthaving the following composition:

NaCIO 744 gm/kg NaClO l I do. NaCI I96 do. NaOH 1 do. Na CQ, 41 do. H 07 do.

are withdrawn via the granule discharge tube.

The physical characteristics of the granules obtained are as follows:

particle size: diameter between 0.5 and 0.6 mm

freely flowing apparent specific weight: 1.3

kg/dm dissolution rate: total dissolution of 10 gm in one liter of waterat 15C within 45 secs.

Compaction does not occur when this process is used because the scraperacts as a stirrer, breaking up the granules into seeds. The end productis perfectly uniform and always has the same chemical composition andphysical properties. Depending upon the operating conditions selected, aproduct containing only 0.5 to 1 percent of water can be prepared fromthe solution in a single operation by means of this process.

Of course, this example can be implemented in a number of different wayswithout stepping outside the scope of the invention. A drier with alateral overflow may be used, the solution may be introduced above thefluidized bed, a scraper of another type may be provided or even omittedaltogether. In this case however, special care must be taken to ensurethat the solution disperses properly to form droplets which, on dryingbefore settling on the fluidized particles, will act as seeds for thegeneration of new particles. Either the droplets must be large enough togive new seeds on drying, or seeds must be prepared by breaking theparticles already in the bed mechanically, depending upon the type ofsprayer.

A solution or aqueous medium having a composition other than the one inthe example, particularly a solution containing a variable amount ofsodium chlorite and/or containing salts other than those mentioned canbe processed. The nature of the particles initially present in the drieris immaterial provided that it is a product compatible with chlorite.

EXAMPLE 2 In this example, a description is given of a method forimplementing the invention in which the seeds are prepared in the bed bybreaking up the component particles mechanically. For this purpose anadequate pulverizing air flow rate is chosen.

A drier, comprising a pyrex tube 30 cm in diameter and 1.5 m high,fitted at the base with a gas distribution plate consisting of a plateperforated with holes 2 mm in diameter, is used. No bladed scraper isprovided. The fluidization zone which is 45 cm above the perforatedplate comprises a steam heated pipe bundle of 0.1 m surface area.Granules are discharged from the fluidized bed via a lateral overflow.

The nourishing solution is introduced via a pneumatic atomizer mountedon the wall cm away from the perforated plate. It is dispersed intoextremely fine droplets which are deposited on the fluidized grains,shattered mechanically by the impact produced by the pulverizing jet ofair.

The initial charge of the bed consists of 40 kg of technical chloritegranules (84 percent by weight NaClO of approximately 0.5 mm diameterdrawn from previous manufacture. It may also consist of sodium chloridegranules. This charge is fluidized by passing a 200 standard m lhrstream of air heated to 120C through the perforated plate. The gagepressure of the steam heating the pipe bundle is 2 kg/cm The bedtemperature is thus raised to 60C.

The air flow rate at the atomizer is 10 standard m /hr and carries anaqueous solution consisting (per kg of solution) of 301 gm of NaClO 8 gmNaClO 32 gm of NaCl, 2.7 gm of NaOH and 4.3 gm of Na CO at a rate of l1.7 kilograms of solution per hour.

4 kg per hr. of product are removed automatically via the fluidized bedoverflow. This product consists of granules having an average diameterof approximately 0.5 mm and a free flowing apparent specific weight of1.45 kg/dm. The chemical composition, per kilogram of product, is asfollows: NaClO 844 gm; NaClO 21 gm; NaCl 100 gm; NaOH 0.3 gm; Na CO 25gm.

In this test, the air was not recirculated. The granule overflow outletcould be easily replaced by an elutriation outlet as in the previousexample.

EXAMPLE 3 An apparatus identical to the one described in Example 2 isloaded with an initial charge consisting of 25 kg of sodium chloridefluidized by passing 150 standard m /hr of air raised to 120C through aperforated plate. The steam gage pressure in the pipe bundle is also 2kg/cm The bed temperature is 60C. Air passing through the atomizer at9.5 standard m/hr disperses an aqueous solution consisting (per kg ofsolution) of 271 gm of NaClO under 2 gm of NaClO 9.7 gm of NaCl, 7.7 gmof NaOH, 6.] gm of Na CO and 194 gm of NaNO;, into the bed at the rateof 7 kilograms of solution per hour. After the system has beenoperatingfor 40 hours and practically all the initial NaCl charge has beenremoved, the overflow from the bed yields a solid product consisting(per kg) of 482 gm of NaClO 2 gm max. of NaClO- 48 gm of NaCl, 13.3 gmof NaOH, 14.9 gm of Na CO and 427 gm of NaNO at a rate of 3.4 kg/hr. Theproduct consists of granules of approximately 0.8 mm diameter and has afree flowing apparent specific weight of 1.3 kg/dm. This is sodiumnitrate enriched chlorite with improved stability.

EXAMPLE 4 Instead of preparing the seeds in the bed by means of asuitable pulverizing jet of air, as described in Examples 2 and 3 above,in this example sodium chloride seeds are introduced at a given rate.

The apparatus used is the one employed in the two previous examples. Aninitial charge consisting of 40 kg of percent sodium chlorite isfluidized by air of fluidization raised to C and introduced at the rateof 200 standard m /hr. The steam gage pressure in the pipe bundle is 2kglcm to produce a bed temperature of about 60C. 4 standard m lhr of aircarrying 1 1.7 kg per hour of an aqueous solution containing per kg ofsolution 301 gm of NaClO 8 gm of NaClO 32 gm of NaCl, 2.7 gm of NaOH and4.3 gm of Na CO are fed in via the atomizer. 0.2 kg/hr of solid NaClseeds having an average particle size of 0.187 mm are also introduced.4.2 kg/hr of a solid product comprising, per kg, 800 gm of NaClO- 20 gmof NaClO gm of NaCl, 0.3 gm of NaOH and 25 gm of Na CO are obtained fromthe bed overflow. This product consists of granules of approximately 0.7mm diameter and has a free flowing apparent specific weight of 1.4kg/dm.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

1. A process for the manufacture of granules containing sodium chloritefrom an aqueous liquid medium containing sodium chlorite, comprising thesteps of evaporating water from said medium by passing said medium intoa fluidized bed drier containing a fluidized bed of particles fluidizedwith a carrier gas having a temperature at the base of the fluidized bedof from 120C to less than C, while maintaining in said fluidized bed aconstant presence of seeds smaller in size than the required granulesand maintaining the temperature in the fluidized bed below 80C.

2. A process as claimed in claim 1 wherein the step of maintainingincludes introducing the seeds into the drier from an external source.

3. A process as claimed in claim 1 wherein the step of maintainingincludes forming the seeds in situ in the drier by mechanicallycomminuting granules in the fluidized bed.

4. A process as claimed in claim 1 wherein the step of maintainingincludes forming the seeds in the drier by dessicating individualdroplets obtained by atomizing the aqueous medium.

5. A process as claimed in claim 3 wherein the step of maintainingincludes gas jet feeding the aqueous medium into the bed formechanically comminuting granules in the bed.

6. A process as claimed in claim 1 wherein the step of maintainingincludes moving a scraper on the base of the drier for preventingcompaction of the particles present in the fluidized bed.

- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent No.3,844,726 Dated October 29th, 1974 lnventofls) Denaev'er et 211 It iscertified that error appear s in the above-identified patent and thatsaid Letters Patent are hereby corrected'as shown below:

In the heading of the patent, line 6, change "Selvey & Cie" to So1vay &Cie.-.

Column 6, line 35, deletev "liquid".

Signed and sealed this 7th day of .Januaryl975.

(SEAL) v Attest:

14:00! 1-5. GIBSON JR. c. mas {ALL DANN Attesting Officer Commissionerof Patents FORM Po-1oso (to-s9) USCOMM-DC 6037G-P69 U.S, GOVERNMENT PR NNG OFIICI II! 0-8604,

1. A PROCESS FOR THE MANUFACTURE OF GRANULES CONTAINING SODIUM CHLORITEFROM AN AQUEOUS LIQUID MEDIUM CONTAINING SODIUM CHLORITE, COMPRISING THESTEPS OF EVAPORATING WATER FROM SAID MEDIUM BY PASSING SAID MEDIUM INTOA FLUIDIZED BED DRIER CONTAINING A FLUIDIZED BED OF PARTICLES FLUIDIZEDWITH A CARRIER GAS HAVING A TEMPERATURE AT THE BASE OF THE FLURIDIZEDBED OF FROM 120*C TO LESS THAN 180*C, WHILE MAINTAINING IN SAIDFLURIDIZED BED A CONSTANT PRESENCE OF SEEDS, SMALLER IN SIZE THAN THEREQUIRED GRANULES AND MAINTAINING THE TEMPERATURE IN THE FLUIDIZED BEDBELOW 80*C.
 2. A process as claimed in claim 1 wherein the step ofmaintaining includes introducing the seeds into the drier from anexternal source.
 3. A process as claimed in claim 1 wherein the step ofmaintaining includes forming the seeds in situ in the drier bymechanically comminuting granules in the fluidized bed.
 4. A process asclaimed in claim 1 wherein the step of maintaining includes forming theseeds in the drier by dessicating individual droplets obtained byatomizing the aqueous medium.
 5. A process as claimed in claim 3 whereinthe step of maintaining includes gas jet feeding the aqueous medium intothe bed for mechanically comminuting granules in the bed.
 6. A processas claimed in claim 1 wherein the step of maintaining includes moving ascraper on the base of the drier for preventing compaction of theparticles present in the fluidized bed.